The instruction mnemonics are typically defined by the manufacturer of the CPU. Although anyone could assign their own arbitrary set of mnemonics for a CPU's instruction set, in practice this is seldom done. Assembly languages do not provide many of the useful abstractions of high-level languages, such as memory management, object and other complex data structure support, or string manipulation.
Such features are often available through libraries of assembly code, though. Assembly language is essential when a new CPU is developed since it allows the development of higher-level language compilers for that CPU. Assembly is also required for access to unique and low-level features of a CPU which is why portions of most operating systems must be written using assembly language. Because assembly provides no abstractions, code written with it can run faster than equivalent code written in a high-level programming language.
However, modern optimizing compilers are often better at generating efficient machine code than human-crafted assembly. Finally, writing assembly code is more tedious and therefore more error-prone than using a high-level language. Macros provide short-hand for assembly programmers. The most common macro feature is the substitution macro. This allows the programmer to define his own mnemonic in place of several preexisting mnemonics. When the macro is used, the assembler will substitute the corresponding mnemonics in place of the macro, as if the programmer had included those mnemonics at that point in the source code.
Floating point math using the second register set for temporary variables made possible a substantial speedup. If the and Z80 waveforms for various instructions are examined, it quickly becomes apparent that the Z80 effectively divided its clock by 2 before using it. This is why, for the technology available in any particular year, they had comparable performance but the Z80 used twice as many clock cycles.
The was a tremendously clever design for making effective use of a small number of transistors. The Z80, striving to be a superset of the , was also a clever and powerful design for its time. Actually, the problem was the ALU of the Z was only 4 bits wide [righto. So processing an 8 bit operand required two trips through the ALU, thus incurring twice the number of clocks or half the effective clock rat.
Z 8 bit register adds, 4 clocks equivalent to 2 clocks 16 bit register adds, 11 clocks, with carry, 15 clocks. The slowest instructions 23 clocks are obscure instructions like swap register with memory, or indirect indexed addressing. These were limited by the number of memory accesses needed. I've built hardware and done a lot of assembly level programming on both the Z80 and There is simply no substantial speed difference between them for the level of technology available in any particula. In , the 68k had been out for a few years already and new 8-bit computer designs were doomed.
And then Commodore went on to half inherit, half design the Amiga. Maybe "cobbled together" is too harsh for it, but still. Floppy controller that can decide, per track, whether to work in MFM or RLL but not read a single sector, mind you , more DMA channels than the CPU can handle, and a display processor with a built-in three commands machine language one of which was only ever used by one application ever to change display resolution mid-monitor.
I loved it, but the Amiga gave the impression that it was designed by engineers that couldn't make up their mind on what choice to make, so they created hardware that would offload all decisions to software. One last anecdote. Many have heard of the famous "Guru meditation". What only Amiga users know is that you knew one was coming because the power led would blink three times. Yes, the power led was software controlled, making the Amiga the first ever computer that could play dead. It's not possible to turn it off completely to simulate the computer being dead.
It's also possible to read a single sector, but that would require starting the DMA on a timer so it's more cumbersome than reading the entire track and it's not guaranteed to be faster since it's a spinning media. The memory is there so reading a single sector is just pointless. The order of the bits is interleaved on Amiga formatted disks to allow for blitter accelerated MFM- de coding. The original Amiga , including the early Kickstart 1. If you don't believe me, you are welcome to visit me. I still have my original machine in more or less working order.
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You are correct that later models would not turn it off completely, but rather only dim it. I only remembered that fact after I hit Send, and thought no one will be anal enough to demand a clarification. You can keep your ancient 1. I have the shining new 2. If I remember correctly changing display modes mid scan was often done so that workbench could do things like display HAM images in windows. All three were used though and it was used for many things such as sprites and the above mentioned screen mode changes.
MOVE put data in pretty much any register such as changing the location. You misremember. The Copper code to change display modes took several scan-lines to run. Having a window with different display mode was impossible.
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You could, and did, have a UI construct called a "screen", which had its own display mode. You could drag a screen down and see another screen behind it. If you know differently, please provide further details. SKIP does seem a bit limited if it is only one entry that it skips. So how did workbench give provide windows containing HAM8 images or where they only full screen windows with a menu bar? I was using PC's back then but I was most impressed with a flatmates Amiga. Shame it struggled to run Elite :.
Menus on the Amiga were bound to the screen, not the window. You are probably remembering a full-window. You got a partial answer. The commands: MOVE: move immediate value into copper register. These included such actions as where in memory the video memory was i. WAIT: wait for the screen update to reach a certain point. There was a mask arg. Amstrad CPC was very successful, especially popular in Europe - cheap price as a dedicated monitor was always bundled and a floppy drive was integrated, whereas other stuff like C64, Spectrum etc.
It's not a killer machine, though. Rudimentary sound and no sprites - but it was colorful, with 16 colors out of a 32 color palette much better than 8 fixed colors on some of the 8bit crap :p Then it did have an upgrade that made it a "killer 8-bit. This is what I came in here to say. They guy who designed the chip is still alive. Just shoot him a email, phone call, or smoke signals and just ask him. I'm going to go out on a limb here and say there is probably a logical reason behind the arrangement and not some conspiracy or something.
The Z80 is still manufactured in classic form. It may be considered a trade secret and Faggin might not be at liberty to divulge anything about the inner workings of the chip without you signing an NDA. Not only is it still manufactured, but it is still used.
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There is a good probability that your DVD burner has a Z80 in it running the show. The is a great example of a 'limited' RISC design, and quite an efficient one. I'm looking forward to the Z80 version, myself. If you had read the article you would know that it is part of an effort to deconstruct the Z80 using optical information and yes they can see all the transistors although identifying them and thier function can be tricky as they were layed out by hand to minimise the space needed.
I have no connection to the project but reading some of the pages on the site are quite interesting if you are electronics minded. Why didn't they just ask Federico Faggin? According to Wikipedia, he's still alive. Interviews: Federico Faggin [wikipedia. The Z was a great chip and overall system design supported by very capable support peripheral chips in that family. The best part of working with it, is Zilog's Documentation, which was very well written and demonstrated the consistency of the entire product line in terms of it's functional programming interfaces.
There really is not any need to 'reverse engineer' the chip, everything you need to know is freely available already. I think this article and author means to say "Here are some plausible possible reasons behind some of these physical implementation decisions While I agree, I wonder if this is actually true.
To what extend does. I think it may be somewhat daunting for a first-year student to go through the learning curve of what would effectively be debugging and optimizing code for an embedded platform Also, just calling the math library r. For all others it might not matter so much how the compiler and the OS handle memory allocations and the like, and it may be more useful to focus on the program structure instead of the implementation on the CPU.
With a cache miss costing cycles more or less and a trip to L2 being more expensive than computing a square root, our choices with regard to memory layout are possibly MORE crucial now to getting decent economy and performance out of the machines we have today. With programs generally being much much larger many such optimisations can just be lost in the noise.
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In some domains it is still useful but even more difficult than it was in times gone by. I am not disagreeing with you but some of the things I pointed out above are varibles with respect to harware and most of them DO affect memory locality. If you make an assmption that x parts of data are localy cached you can be truely wrong when run on a compatable chip with a different cache layout or even the same chip but with a different offset that is only partialy aligned with the cache. Some algorithms in general tend to keep the data used close to gether and they may benifit.
Some algorihms uses dat. You say that it is remarkable how uniform current platforms are? I am interested as to why you think that as even on just x86 and x64 ther. Cheap memory accesses compared to instruction latency, over your whole memory space. Memory locality basically doesn't matter.
Branching is also almost free, since you are not pipelined at all. If you would extrapolate a Z80 machine to multi-gigahertz and multi-gigabyte you would get a much simpler low-level structure than you actually have. Some of the lessons learned regarding being frugal make sense, but you will also learn a lot of tricks that are either directly counter-productive, or at the very least steal your attention from what you should be concerned with, even in those very cases where you are really focusing on performance and power efficiency in addition to the myriad of valid cases where developer productivity is simply more important than optimality.
It used to be that you couldn't pre-calculate everything since you didn't have enough storage. These days, you shouldn't pre-calculate everything since it will actually be cheaper to do it again rather than risk hitting main memory with a tremendous amount of random accesses, or even worse, swap. Up to some quite serious size data sets a flat data structure with fully sequential accesses can turn out to be preferable to something like a binary tree with multi-level indirections.
Add to it the great book Programming the Z80 [freecomputerbooks. Personally I think that it should be in the collection of books even if you don't aim to program specifically for the Z80 because it explains a lot of general CPU architecture and logic as well. While you can still buy a lot of embedded processors in DIP format, I haven't considered it very much - but yes, those were the days.
Now you can just buy reasonable micros on affordable eval boards or other very simple boards with plenty of wire-wrap headers or solder points. You can cut a lot of the mundane work like breadboarding a voltage regulator, memory, osc, serial transceiver, etc. Though I was a sixer, I miss those days. Put a or ?
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Did wonderful things with that. That was one hell of a chip. So quick to code on. It ran BASIC so slowly that you could actually read the code about as fast as it executed, so I was "forced" to learn assembly language. I was amazed by how fast it was- it ran a million operations in just a few seconds! Then you had to POKE each assembly instruction into the comment, starting at for the first "A".
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